Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
-
Neurons located in the border region between the interpolaris and caudalis subdivisions of the spinal trigeminal nucleus (Vi/Vc) are second order neurons of the corneal reflex, receiving corneal afferents and projecting to the lid closing, orbicularis oculi (OO) motoneurons. Recordings of Vi/Vc neurons identified by antidromic activation from stimulation of the facial nucleus and non-identified Vi/Vc neurons reveal two neuron types, phasic and tonic. Corneal stimulation elicits Adelta latency action potentials that occur early enough to initiate OO contraction and C-fiber latency action potentials that can modulate the end of the blink in phasic Vi/Vc neurons. ⋯ Vi/Vc neuron discharge, however, is slightly larger for the second blink. Our data indicate that second-order Vi/Vc neurons do not determine the specific pattern of OO muscle activity; rather Vi/Vc neurons initiate OO motoneuron discharge and program the activity of another circuit that generates the late phase of the blink. The Vc/C1 suppression of Vi/Vc neurons suggests that the Vc/C1 region provides an "internal model" of the intended blink.
-
Successive tactile stimuli, delivered one to each hand, are referred to spatial representation before they are ordered in time (Yamamoto and Kitazawa in Nat Neurosci 4:759-765 2001a). In the present study, we examined if this applies even when they are delivered unilaterally to fingers of a single hand. Tactile stimuli were delivered left-to-rightward relative to the body (2nd-3rd-4th) or in reverse with stimulus onset asynchrony of 100 ms. ⋯ It was greater than 95% when the direction of visual stimuli matched that of the tactile stimuli, but less than 50% when they were opposite to each other. When the right hand was rotated counterclockwise on the horizontal plane (90 degrees ) so that the fingers were pointing to the left, the preferred direction of visual stimuli that yielded the peak correct judgment was also rotated, although not to the full extent. These results show that subjects cannot be basing their tactile temporal order judgment solely on a somatotopic map, but rather on a spatial map on which both visual and tactile signals converge.
-
It has been shown on hand muscles in normal subjects that paired associative stimulation (PAS) combining peripheral nerve stimulation and transcranial magnetic stimulation (TMS) induces lasting changes in cortical motor excitability (Stefan et al., Brain 123 (Pt3):572-584, 2000). Because the motor recovery of distal upper limb and particularly wrist extension in post-stroke patients is one of the major rehabilitation challenge, we investigate here the effect of one session of paired associative stimulation on the excitability of the corticospinal projection to extensor carpi radialis (ECR) muscle (motor evoked potential size) before and after PAS in 17 healthy subjects and in two patients 5 months after stroke. The time course, the topographical specificity, changes in rest motor threshold (RMT), short intracortical inhibition and intracortical facilitation (SICI and ICF), the respective role of cutaneous and muscular afferents and the effect of a prolonged peripheral stimulation alone were also studied in normal subjects. ⋯ However, it has been observed in dystonic patients (Quartarone et al., Brain 126:2586-2596, 2003). This suggests that other mechanisms like changes in membrane excitability could be involved in ECR facilitation after PAS. Further studies performed on patients using daily repeated PAS protocols and showing a functional improvement in hand motor function will be necessary to confirm that this technique could be relevant in motor rehabilitation, at least for some selected patients.
-
The aggregation of beta-amyloid to plaques in the brain is one of the hallmarks of Alzheimer disease (AD). Numerous studies have tried to elucidate to what degree amyloid peptides play a role in the neurodegenerative developments seen in AD. While most studies report an effect of amyloid on neural activity and cognitive abilities of rodents, there have been many inconsistencies in the results. ⋯ The aggregation studies showed that amyloid (25-35) aggregated within hours, while amyloid (35-25) did not. These results show that the genetic background and the stimulation protocol are important variables that greatly influence the experimental outcome. The fact that amyloid (25-35) aggregated quickly and showed neurophysiological effects, while amyloid (35-25) did not aggregate and did not show any effects indicates that the state of aggregation plays an important role in the physiological effects.
-
Several functional MR imaging studies evaluating the lateralisation of linguistic functions in patients who underwent Wada testing have been reported. There is extensive variance in the Laterality index (LI) calculation across the studies, and the optimal calculation method remains unclear. We attempted to calculate the LI in different ways in the same subjects, in order to find the LI calculation method with the highest correlation to the Wada test. ⋯ First, the LIs were calculated from the ROIs using a previously reported method (simple suprathreshold count). Next, we used several new methods of LI calculation (t-weighting of voxels, methods independent of the choice of the statistical threshold, etc.) The most significant correlation with Wada was proven in the LIs that were evaluated from Broca's area (up to R = 0.94, P = 1 x 10(-7)). However, the new LI calculation methods used in the present study did not produce a statistically significant benefit in comparison to previously reported methods.